Calcium waves in agarose gel with cell organelles: Implications of the velocity curvature relationship

Calcium oscillations and waves have been observed not only in several types of living cells but also in less complex systems of isolated cell organell es. Here we report the determination of apparent Ca2+ diffusion coefficient s in a novel excitable medium of agarose gel with homogeneously distributed vesicles of skeletal sarcoplasmic reticulum. Spatiotemporal calcium patter ns were visualized by confocal laser scanning fluorescence microscopy. To o btain characteristic parameters of the velocity curvature relationship, nam ely, apparent diffusion coefficient, velocity of plane calcium waves, and c ritical radius, positively and negatively curved wave fronts were analyzed. It is demonstrated that gel-immobilized cell organelles reveal features of an excitable medium. Apparent Ca2+ diffusion coefficients of the in vitro system, both in the absence or in the presence of mitochondria, were found to be higher than in cardiac myocytes and lower than in unbuffered agarose gel. Plane calcium waves propagated markedly slower in the in vitro system than in rat cardiac myocytes. Whereas mitochondria significantly reduced th e apparent Ca2+ diffusion coefficient of the in vitro system, propagation v elocity and critical size of calcium waves were found to be nearly unchange d. These results suggest that calcium wave propagation depends on the kinet ics of calcium release rather than on diffusion.